[JPNet]

The number of outs you have is the same regardless of whether there are 2 cards to come or only 1, for instance, if you have 4 to a flush such as 2 spades in your hand and 2 more on the board, you have 9 outs that will complete your flush. If you don't make your flush on the turn, you still have 9 outs to make the flush on the river.
I assume that what you really want to know is what your odds are with 2 cards to come vs 1 card to come. There are shortcuts that will give you an answer that is close, but the odds you get by these methods are close, not correct, so you need to understand how close, and when. Mainly, taking the shortcut route will be pretty close if you have 10 or fewer outs, and not so close if you have more than 10 outs.
So, for instance, if you have a flush draw with 1 card to come, on the river for instance, there are 9 cards that will help, and 37 that will not, so your odds are a little worse than 4:1 against making the flush. If you have 2 cards to come, you can multiply your outs by 2, and get 18. On the flop, there are 38 cards that will not help you, so 38:18, or 2.11:1 against making the flush. Note that the actual odds are 1.9:1 against.
Anoter way of taking a shortcut is to caculate the odds with 1 card to come and then divide by 2. So with 9 outs, and 38 cards that don't help, your odds are about 4.1:1 against making it. Divide by 2 and you have about 2:1 against making it.
Note that taking the shortcut approach with 2 outs gives you an answer of 11.25:1 against, while the real answer is 11:1 against, at 10 outs, the shortcut gives you 1.85:1 against vs the correct answer of 1.6:1 and at 15 outs, the shortcut gives you 1.07:1 vs .85:1 against.
The better way to accomplish what you want is to check a table of outs vs odds and memorize the more important ones.
Ed Miller has an excellent section on outs in SSH, Mike Petriv's book Hold'em Odds Book is excellent, I have a lot of material on my web site, and I am sure there are many other sources.